This application is based on and incorporates herein by reference Japanese Patent Applications No. 2000-19303 filed Jan. 27, 2000 and No. 2000-363045 filed Nov. 29, 2000.
The present invention relates to an engine control unit, and particularly to an engine control unit which determines cylinders to be controlled of an engine.
An engine control unit (ECU) is an electronic control unit for performing controls such as fuel injection control, ignition timing control, and idle speed control to operate an engine in an optimum state. Specifically, signals from various sensors for sensing engine operating states such as crank angle sensor and engine coolant temperature sensor are supplied to the ECU to control an optimum fuel injection amount, injection timing, ignition timing, and the like.
Controls synchronized with the engine speed such as ignition control and injection control, that is, controls synchronized with a crankshaft rotation position are performed by generating a signal of ignition pulses or the like after elapse of offset (delay) time from a predetermined crankshaft position indicated by the edge of a crank signal. Further, a cylinder to be controlled with respect to fuel injection and ignition must be determined accurately from time to time during engine operation.
It is, however, necessary to perform an arithmetic operation for converting the angle to time. There is a demand for reduction in processing load and improvement in accuracy.
It is therefore an object of the present invention to provide an engine control unit with reduced processing load and improved accuracy and, moreover, capable of properly controlling the engine even when a cylinder determination signal includes noises.
According to the present invention, a crank signal and a can signal are generated by a crank angle sensor and a cam angle sensor in synchronism with rotation of a crankshaft and a camshaft of an engine, respectively. The crank signal is generated to have a front pulse missing portion and a back pulse missing portion in a pulse train of every predetermined angle interval. The cam signal is generated to have different levels in the pulse missing portions of the crank signal. A level different from that in the pulse missing portion continues for a period of predetermined angles before the pulse missing portion. A microcomputer determines each of the front and back pulse missing portions in the crank signal on the basis of the level of the cam signal in the pulse missing portion of the crank signal in two cycles of the rotation of the crankshaft of the engine and the duration of the different level before the pulse missing portion.